feat: add basic tests for local variables (#65)

## what
- generate basic tests for logic performed in `locals { ... }`
- test the generated `userdata.sh` script.

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: westonplatter

.gitignore

@@ -44,3 +44,8 @@ backend.tf.json
 **/*.bak
 **/*.*swp
 **/.DS_Store
+
+.cursor/
+
+.claude/
+CLAUDE.md

tests/locals.tftest.hcl

@@ -0,0 +1,94 @@
+# Common variables used across all test runs
+variables {
+  vpc_id     = "vpc-test123"
+  subnet_ids = ["subnet-test123"]
+  namespace  = "test"
+  name       = "tailscale"
+}
+
+# Mock tailscale provider because it expects a real authentication (so we provide it a fake tailscale_tailnet_key)
+mock_provider "tailscale" {
+  mock_resource "tailscale_tailnet_key" {
+    defaults = {
+      key = "fake-tailscale-tailnet-key"
+    }
+  }
+  override_resource {
+    target = tailscale_tailnet_key.default
+    values = {
+      key = "fake-tailscale-tailnet-key"
+    }
+  }
+}
+
+mock_provider "aws" {
+  mock_data "aws_iam_policy_document" {
+    defaults = {
+      json = "{\"Version\":\"2012-10-17\",\"Statement\":[{\"Effect\":\"Allow\",\"Principal\":{\"Service\":\"ec2.amazonaws.com\"},\"Action\":\"sts:AssumeRole\"}]}"
+    }
+  }
+  mock_resource "aws_launch_template" {
+    defaults = {
+      id = "lt-mock123456789"
+    }
+  }
+}
+
+run "test_primary_tag_provided" {
+  command = plan
+
+  variables {
+    primary_tag = "test-router"
+  }
+
+  # Test that the primary_tag is set to the provided value
+  assert {
+    condition     = local.primary_tag == "test-router"
+    error_message = "Expected local.primary_tag to be 'test-router'"
+  }
+
+  # Test that the prefixed_primary_tag is set to the provided value
+  assert {
+    condition     = local.prefixed_primary_tag == "tag:test-router"
+    error_message = "Expected local.prefixed_primary_tag to be 'tag:test-router'"
+  }
+}
+
+run "test_local_userdata_rendered_template" {
+  command = apply # because we need access to the tailscale_tailnet_key.default.key value
+
+  variables {
+    primary_tag = "test-router"
+    additional_tags = ["test-tag1", "test-tag2"]
+  }
+
+  # Ensure userdata script contains `tailscale up` and tailscale key
+  assert {
+    condition = (
+      strcontains(local.userdata, "tailscale up") &&
+      strcontains(local.userdata, "--authkey=fake-tailscale-tailnet-key") &&
+      strcontains(local.userdata, "SystemMaxUse=200M")
+    )
+    error_message = "Expected userdata to contain tailscale up command, authkey, and journald config"
+  }
+
+  # Ensure userdata script contains transformed additional tags
+  assert {
+    condition = strcontains(local.userdata, "tag:test-tag1") && strcontains(local.userdata, "tag:test-tag2")
+    error_message = "Expected userdata to contain additional tags"
+  }
+}
+
+run "test_tailscaled_extra_flags" {
+  command = apply # because we need access to the tailscale_tailnet_key.default.key value
+
+  variables {
+    tailscaled_extra_flags = ["--state=mem:", "--verbose=1"]
+  }
+
+  # Test that tailscaled_extra_flags are rendered in userdata
+  assert {
+    condition = strcontains(local.userdata, "--state=mem:") && strcontains(local.userdata, "--verbose=1")
+    error_message = "Expected userdata to contain tailscaled extra flags"
+  }
+}